1. Field of the Invention
The present invention relates to a light emitting diode driving circuit, a backlight unit and a liquid crystal display incorporating the same. More particularly, the present invention relates to a light emitting diode driving circuit having a peripheral circuit unit for enhancing the reliability and efficiency of a pulse width modulation (“PWM”) control unit included therein, and a backlight unit and liquid crystal display incorporating the same.
2. Description of the Related Art
Light emitting diodes (“LEDs”), fluorescent lamps, and metal halide lamps are commonly used as backlight light sources for liquid crystal displays (“LCDs”). Of the different types of backlight light sources, “LEDs” have long life, require no additional inverter, are lightweight and thin, can uniformly emit light and have superior low power consumption. Thus, “LEDs” are frequently used as backlight light sources for small and medium sized “LCDs”.
In general, switching power sources are used for driving “LEDs” used as backlight light sources in “LCDs”. A switching power source is characterized by reduced power losses as they are operated in a switching mode, and thus small loss and high efficiency may be achieved as small, lightweight and high frequency transformers are employed. In addition, a switching power source may be utilized in various countries having different standard operating voltages without change of taps or circuit constants, since such devices have a wide range of input voltages associated therewith. Furthermore, these switching power sources are essential for communication devices powered by DC power sources, or for DC to DC converters in mobile equipment or other types of portable devices in which DC power sources (e.g., batteries or storage batteries) are used. Accordingly, the use of switching power sources has increased in accordance with the increasing demands of decreasing energy consumption.
Presently, there are a variety of types of switching power sources in existence, depending on specific circuit configurations or control methods of DC to DC converters. In one application of a switching power source, constant current control is used to control a power source for supplying a constant voltage to a load, regardless of time and amplitude variations. Such a device is referred to as a DC power supply. Since a change in output voltage due to load variations may occur in such a DC power supply, a feedback circuit such as a “PWM” control circuit is included within the DC power supply to obtain a stabilized power source.
However, a DC power supply typically generates noise in switching elements, rectifying diodes, transformers, choke coils and the like. In turn, such noise has an influence on other circuits (e.g., “PWM” control circuits), thus hindering the capability of maintaining a stabilized power source. Accordingly, is desirable to be able to minimize the influence of noise on “PWM” control circuits used in applications such as, for example, LED driving circuits for “LCD” backlight sources.